1. Field of the Invention
The present invention relates to a semiconductor device used in an ultrahigh frequency band and semiconductor apparatus using the semiconductor device or devices.
2. Description of the Related Art
A semiconductor chip, such as a small signal amplifying chip, is manufactured as a semiconductor device encapsulated with various materials and, primarily, a mold resin type and ceramics type are used as such a package.
The semiconductor device using a small signal amplifying chip demands a low noise characteristic and high gain characteristic and the electrical characteristic of the semiconductor device can be normally represented by an equivalent circuit as shown in FIG. 1. In FIG. 1, a semiconductor chip is indicated by reference numeral 105 and the circuit contains various high-frequency-like parasitic parameters, causing increased noise and lowered gain.
In a semiconductor device including a small signal amplifying chip, a matching circuit is juxtaposed near the device normally mounted on a board in order to minimize the noise figure or maximize the gain. Therefore, decreasing, among the aforementioned parasitic parameter components, a parasitic parameter component not compensated for by the matching circuit is important to derive out the characteristics from the semiconductor device. The parasitic parameters not compensated for by the matching circuit is comprised of, in a practical embodiment, a pure resistance and an inductance component in series with the ground of the semiconductor chip. In particular, the loss component at an input section exerts a direct influence over the noise figure of the mounted semiconductor chip and an inductance connected in series with a ground electrode acts as a negative feedback, thus leading to a lowered gain.
A conventional mold type package is shown in FIG. 2 by way of example. In a semiconductor device 100, a semiconductor chip 101 is connected by bonding wires 104a to a ground electrode 102. The portions of ground electrode 102, being brought out from the two opposed sides of the semiconductor device 100, is bent flush with the bottom surface of the device so that the ground electrode may be mounted on a circuit board. Those opposed electrodes 103,103 are provided in a 90.degree.-intersecting relation to the ground electrode 102 so that they serve as an input/output electrodes. The electrodes 103 are connected by bonding wires 104b to the semiconductor chip 101. The portions of the electrodes 103, being brought out from the remaining opposed sides of the device 100, are bent as in the case of the ground electrode 102, that is, bent flush with the bottom surface of the device.
Aforementioned loss can be divided into dielectric loss and metal loss.
A resin used for the semiconductor device has a dielectric loss tangent about 10 times as great as that of alumina and the dielectric loss of the mold resin type becomes greater than the ceramics type. For the mold resin type package, the input section is formed of a metal piece (lead frame) and the metal loss is small compared with the ceramics type package. Taken this into consideration, the total loss of the input section little varies between the ceramics type and the mold resin type. For a package of an outer configuration of 1.78 mm square generally in use, for example, the loss is about 0.05 dB. In a currently developed highest-level low-noise amplifier type, the noise figure is about 0.5 dB and an influence of package loss upon the characteristic of the whole semiconductor device is a little less than 10%. However, the gain is greatly influenced from the inductance grounded.
FIG. 3 shows the result of calculation made on the characteristic of a gain while varying the value of the inductance grounded Ls in the circuit shown in FIG. 1. In the graph shown in FIG. 3, the curves b, c, d, e and f correspond to the inductance values being 0.01, 0.05, 0.09, 0.13 and 0.17 nH, respectively, and the curve a denotes the characteristic of a semiconductor chip itself (bare chip) used for the calculation. For the mold type package of FIG. 2 mounted on the board, the ground inductance was 0.17 nH upon evaluation on the characteristic of the equivalent circuit. This corresponds to the curve f in FIG. 3. Upon comparison between this characteristic and the characteristic (curve a) of the chip itself shown in FIG. 3 it is found that, for 12 GHz for instance, the gain was decreased by as low as 5 dB.
It is to be noted that such a mold type package is usually molded by a transfer molding method. A lead frame (electrode) used in this method is chiefly formed by etching technique or press working and the shape of the lead frame is restricted to some extent. The shape of the lead frame is also restricted in the cases where, in order to readily effect a wire bonding, the lead frame is thinly formed and terminal electrodes (pads) are located in the same plane.
A leadless chip carrier (LCC) and quad flat package (QFP) are known as the examples of the ceramics type package. In the case of LCC, the inner leads for signals are electrically connected to a connection electrode on the lower surface of the package by a metallized pattern provided at the side surfaces of the package. Since, in this way, the signal leads are provided by metallization from the side surfaces to the rear surface of the package, the lower surface of the package cannot be constructed by a metal piece. In the case of LCC, there is some limitation to reducing the inductance grounded.
On the other hand, QFP has generally been employed as a surface-mounting type package for high-frequency chip because a parasitic parameter in the connection section is small compared with through hole mount device such as PGA (pin grid array) or DIP (dual in-line package). In the case of QFP, the signal leads brought out from inside the package are electrically connected to the printed circuit board by the lead frame brazed to the package.
In the device for such high-frequency chip, however, a greater influence is exerted, on many occasions, over the characteristics of the device. In order to reduce the inductance, the lower surface of the device, together with the lead frame, is contacted with the circuit board to achieve a connection to an external ground electrode in which case, in order to also improve a heat dissipation characteristic, the lower surface of the device is composed of a piece made of an alloy, such as a copper-tungsten alloy. In the case of QFP, the inductance grounded can be made smaller, but a greater mounting area is required for the lead frame. The device involves its characteristic degradation resulting from a fall in its own resonance frequency. The unit cost is also raised.
In the semiconductor device comprised of a package encapsulated with a resin, etc., having a small signal amplifying chip mounted on the ground electrode, the gain is largely lowered compared with that of a bare chip, thus presenting a problem.
As a device with leads brought out from a surface facing to a surface of a circuit board, a device of a TO-type or the like is conventionally known in MAXIM 1989 Integrated Circuits Data Book. Since the device has relatively long leads, a greater inductance is involved and, further, the leads are mounted on the circuit board by insertion, thus presenting a problem from the standpoint of manufacturing steps. Since the device is used over a low frequency of a range of several ten MHz, it is not fitted to the application to an ultrahigh frequency of about 1 to several ten GHz.